Integrated circuit fabrication generally consists of a series of process steps or stages, for example, photolithography, etch, strip, diffusion, ion implantation, deposition, and chemical mechanical planarization (also known as chemical mechanical polishing, or “CMP”). At each step or stage, inspections and measurements are conducted to monitor the equipment which performs the process as well as the overall process, individual processes, and interaction and integration among individual processes.
Typically supporting the integrated circuit fabrication process is a complex infrastructure of, for example, materials supply, waste treatment, support, logistics and automation. Integrated circuit fabrication processes tend to utilize one of the cleanest environments in the world.
Integrated circuits are typically made on or in a semiconductor substrate that is commonly known as a wafer. A wafer is a substantially round, thin disk, having diameters such as four inches to twelve inches, and thicknesses in the range of two to three quarters of a millimeter. During the fabrication process, materials or layers are added, treated and/or patterned on or in the wafer to form the integrated circuits.
With reference to FIG. 1, the equipment employed to fabricate integrated circuits may be classified, in a functional manner, into two categories:                Processing equipment (“PE”): this type of equipment creates physical or chemical changes to a wafer; for example, equipment used in performing photolithography, etch, strip, diffusion, ion implantation, deposition and/or chemical mechanical polishing (“CMP”).        Monitoring equipment (“ME”): this type of equipment measures and/or analyzes certain parameters on a processed product or test wafer in order to, among other things, ensure the process(es) has behaved according to specification. That is, MEs measure, evaluate and/or analyze the integrity of the process(es). For example, MEs include equipment used in conducting defect inspection, surface profiling, optical or other types of microscopy. Notably, certain MEs may cause or require changes to measurement sample wafers. For example, an SEM may require a measurement sample wafer be cross-sectioned in order to analyze its profile. Indeed, these samples may be special test wafers, instead of product wafers.        
Generally, conventional monitoring equipment consists of the following subsystems or components:                1. Source units—i.e., units that generate and direct the technique and mechanism of interrogation (for example, electromagnetic wave, charged particles, electrical voltages and currents, etc.) towards the measurement sample wafer. The technique of interrogation depends on the parameter being measured. For example, when measuring the smallest feature sizes made on an integrated circuit, known as Critical Dimension (“CD”), an electron beam may be used to resolve features as small as those used in integrated circuit manufacturing.        2. Sensing units—i.e., devices or circuitry that samples, senses, detects and/or measures the response of the measurement sample to the interrogation from/by the source unit. The sensing units may include, for example, temperature, light sensors, image sensors, charged particle sensors, voltage and current meters, and/or detectors. In the example of measuring CD using SEM, the electron beam reflected or scattered from the wafer is collected to form a high-resolution image of the features or profile on the wafer surface.        3. Analysis and user interface units—i.e., units that rely on a general purpose or specialized computer, algorithms and software to analyze information collected by the sensing units and present the results in a suitable format to, for example, process engineers or higher-level yield management and analysis software.        4. Wafer handling units—i.e., units that are responsible for handling the measurement samples, most likely in the wafer format, including, for example, loading, unloading, aligning, and conditioning wafers.        
Given the number of different parameters that are measured or inspected in assessing the integrity of a process, there are many different types of MEs employed in a typical semiconductor manufacturing facility. The MEs may utilize different physical principles to detect, inspect or measure one or more parameters that may be used to characterize the process. For example, thin-film thickness measurement tools measure the thin films deposited on the wafer utilizing, for example, ellipsometry, reflectometry, or sheet resistance.